Mts1 is a unique gene isolated from metastatic mammary carcinomas belong to the S100 family of calcium binding proteins. It is selectively expressed during embryogenesis and metastasis. Both the murine as well as human cDNAs have been cloned and characterized in our laboratory. It is encoded in humans on chromosome 1 and on chromosome 3 in the murine system. The gene product is an approximately 10 KD protein moiety, with very high homology to the Ca++ binding domain of the other members of S100 family of proteins, which are highly conserved. In view of the relevance of this gene product to the process of invasion, motility, embryonic transplantation, and metastasis, we propose to study the biological significance of this gene using a variety of molecular and cell biological techniques. Mouse and human cDNAs will be overexpressed, both in bacterial as well as eukaryotic expression systems, and the protein obtained will be used to generate highly specific mono and polyclonal antibodies. To determine whether there is a causal relationship between mts1 expression and metastatic phenotype, additional copies of the mouse mts1 will be introduced into the mouse benign breast tumor cell line CSML0 by DNA transfection techniques. Similarly, constructs containing Mts1 cDNA in opposite orientation will be introduced into the highly metastatic CSML100 cell line. In addition, these transfectants will be cotransfected with beta-gal gene to be used as a visual, sensitive marker to detect mice metastases. These permanently transfected cell lines along with their parent control lines will be utilized in testing multiple aspects of the tumorigenic and metastatic phenotype, i.e. growth rates, invasiveness, and motility, levels of proteolytic enzymes, etc. Using immunohistochemical and in situ hybridization techniques, mts1 expression patterns will be generated on murine embryonic tissue (days 5-10) when trophoblasts are the most invasive) to examine the correlation between invasiveness and mts1 expression. Serial sections of the tw73 implantation defective mouse embryonic and extraembryonic tissues (days 5-10) will also be tested similarly. Human trophoblast cultures (villous cultures of the first trimester human placenta) will be used to examine mts1 gene involvement in cellular differentiation, motility and invasiveness during embryonic implantation. Similar studies will be conducted on tumor tissues at various stages of tumor progression to evaluate mts1 protein's role in aspects of tumor metastasis.